As generally known in the art, transferable conveyer belts or other transfer means are used to transfer substrates between respective processes for manufacturing various types of circuit boards or panels. In addition, various means are used to accurately position the transferred substrates before each process starts.
The accurate positioning of substrates has higher importance in the case of processes for manufacturing semiconductors or LCD panels, which require a high level of precision. As used herein, an LCD (Liquid Crystal Display) refers to a device for displaying images, which includes two substrates facing each other and having their own electrodes, and liquid crystals injected between both substrates so that, when a voltage is applied to both electrodes, the resulting electric field moves the liquid crystal molecules and varies the transmittance of light.
Processes for manufacturing a liquid crystal panel (also referred to as cell processes) will now be described briefly.
The cell processes include an orientation process for orienting liquid crystals in a direction with regard to an array substrate, on which thin film transistors are arranged, and a color filter substrate, on which color filters are formed; a cell gap forming process for bonding both substrates to each other to maintain a predetermined gap; a cell cutting process; and a liquid crystal injection process.
Each cell process will be described in more detail with reference to FIG. 1.
In the first process, i.e. in the orientation film forming process, the array substrate, which has thin film transistors arranged for respective pixels, and the color filter substrate, which has red, green, and blue color filters formed to correspond to respective pixels of the array substrate, are coated with polyimide, which is a type of polymer, to form an orientation film (s1). A roll coating method is commonly used to print a polyimide orientation film of a uniform thickness in a predetermined pattern on the entire surface of the array substrate and the color filter substrate. Then, both substrates are subjected to preliminary drying and baking processes to harden the orientation film.
The upper and lower substrates, which have a hardened orientation film formed thereon, proceed to the second cell process, i.e. rubbing process (s2). The surface of the hardened orientation film is rubbed against a rubbing cloth at constant pressure and rate to align the polymer chains on the surface in a predetermined direction. The rubbing process is an importance process for determining the initial direction of arrangement of liquid crystals and guaranteeing that they are driven normally and are endowed with uniform display characteristics.
After the rubbing process is over, both substrates are subjected to the third step, i.e. processes for forming a seal pattern, applying silver (Ag), and scattering spacers (s3). The lower substrate, i.e. the array substrate, is subjected to the seal pattern forming and silver application processes, while the upper substrate, i.e. the color filter substrate, is subjected to the spacer scattering process. Alternatively, the color filter substrate is subjected to the seal pattern forming and silver application processes, while the array substrate is subjected to the spacer scattering process. The seal pattern of a liquid crystal panel has the role of forming a gap into which liquid crystals are injected, as well as the role of preventing the injected liquid crystals from leaking. In the seal pattern forming process, sealant (a type of thermosetting resin) is used to form a desired pattern on the edge of the substrate according to a screen mask method, which employs a seal screen printing device, or a dispenser method, which employs a seal dispensing device. The dispenser method has recently gained popularity in line with the current trends toward larger substrates.
After the seal pattern has been formed, the array substrate (color filter substrate) is subjected to the silver application process. In this process, a predetermined amount of silver (Ag) paste is applied at predetermined points on the array substrate for electric conductance between the upper and lower substrates.
While the array substrate (color filter substrate) undergoes the seal pattern forming and silver application processes, the color filter substrate (array substrate) is subjected to the spacer scattering process for scattering ball spacers at a uniform density throughout the entire surface of the substrate so that a cell gap is formed in the active region. Methods for scattering spacers include a dry-type method and a wet-type method. The dry method electrically charges spacers so that they are scattered without clumping together, and is used more often than the latter. It has been recently proposed to form patterned spacers at a predetermined interval on the color filter substrate, while the substrate is manufactured, to maintain a cell gap. In this case, the spacer scattering process is omitted.
After the array substrate (or color filter substrate) has undergone the seal pattern forming and silver application processes, and after the color filter substrate (or array substrate) has undergone the spacer scattering process, the fourth process, i.e. bonding process, starts (s4).
In order to bond the array substrate and the color filter substrate to each other, the color filter pattern of the upper substrate must be accurately aligned with the pixels of the lower substrate (bonding alignment). The degree of bonding alignment is determined based on the margin set for each substrate during design. The bonding margin depends on the extent to which the black matrix on the color filter substrate overlaps the pixel electrodes on the array substrate, and a precision level of a number of micrometers is required. If the bonding alignment of both substrates lies out of the error range, light leaks out. This means that, when the liquid crystal cells are driven, desired screen quality cannot be obtained. After the bonding alignment, the upper and lower substrates are bonded to each other to obtain a circular panel. Even pressure is applied to the circular panel concurrently application of heat to the seal pattern so that the cell gap remains constant and that the seal pattern is hardened.
The circular panel is then cut in the following cell cutting process (s5). In this process, the circular panel created through the preceding steps is cut into unit cells. The cell cutting process includes a scribing process for marking a cutting line on the surface of the circular panel by using a cutting wheel made of diamond or hard metal, the hardness of which is higher than glass substrates, and a breaking process for applying force to the cutting line to break the panel.
The liquid crystal panel, which has been cut into unit cells through the cutting process, is subjected to a liquid crystal injection process (s6). In this process, the interior of the liquid crystal panel, which has a cell gap of a number of micrometers, is vacuumized, and liquid crystals are injected into the liquid crystal panel by using the capillary phenomenon and the difference relative to the atmospheric pressure. After the liquid crystal injection is over, the injection hole is sealed by sealant, which is then irradiated with UV rays for hardening.
Then, shorting bars on the pad of the liquid crystal panel are removed in a grinding process, and the liquid crystal panel is examined to confirm whether it is qualified or not (s7). This completes the processes for manufacturing the liquid crystal panel.
Recent LCD cells, which are manufactured through the above-mentioned processes, tend to have a combination of at least two models of seal patterns 2 and 3 with different sizes in the same substrate 1, as shown in FIG. 2, in connection with the current trends toward larger substrates 1. More particularly, a large model seal pattern 2 is formed as a main pattern for increasing the efficiency in using the area of the substrate 1, and a medium or small model seal pattern 3 is formed in the remaining region.
A seal dispenser device is used to examine and repair such a substrate, which has a seal pattern 2 formed thereon. FIG. 3 partially shows a seal dispenser device including a seal dispenser.
As shown in FIG. 3, an array substrate 1, on which seal patterns 2 and 3 are to be formed, is positioned on a stage 4 of the seal dispenser device 7. Then, the seal dispenser 5, which is positioned above the stage 4 and which is filled with sealant, is aligned and positioned to start forming seal patterns 2 and 3. Based on a program regarding the shape of seal patterns, which has been inputted to the seal dispenser device 7, seal patterns 2 and 3 are formed along the edge of the substrate 1.
The seal dispenser device 7 is equipped with a camera 6 for checking disconnection of the seal patterns 2 and 3 formed on the substrate 1 and measuring their line width. Therefore, after the seal patterns 2 and 3 have been formed, the camera 6 moves along the seal patterns 2 and 3 to check disconnection. If a number of points have been designated in different positions according to respective models, the camera 6 measures the line width of the seal patterns 2 and 3.
Data regarding acceptable line widths of the seal patterns 2 and 3 for respective models has been inputted to the seal dispenser device 7, and is compared with the measured line width data. If the result of comparison lies out of the error range, the alarm is raised, for example, to inform that the formed seal patterns 2 and 3 are defective.
If the seal patterns 2 and 3 have disconnection, liquid crystals may leak after the bonding. If the line width of the seal patterns lies out of the error range, the amount of injected liquid crystals varies, and so does the cell gap. As a result, the thickness of liquid crystals becomes uneven, and the display quality degrades.
As such, the examination and repair processes are very important, and the alignment of the substrate 1 is crucial to the improvement of examination precision.
However, as substrates or panels tend to become larger, it has become increasingly difficult to position the substrate 1, which is transferred by a robot arm and seated on the stage 4, at the accurate alignment point. This necessitates either adjustment of the stage 4 or meticulous adjustment of the large substrate by an adjustment means. However, either case requires a large amount of power. Furthermore, adjustment of the entire substrate 1 takes a long period of time, and lengthens the overall process time.